If liquid water is cooled below 0°C it turns into the solid, ice - Edexcel - GCSE Chemistry Combined Science - Question 1 - 2021 - Paper 1

• the molecules move faster in water than in ice ✔️
• the molecules are arranged regularly in ice but not in water ✔️

This drinking water should not be described as pure water because it contains dissolved solids, meaning it is not solely composed of water molecules. The presence of calcium ions, sodium ions, and hydrogen carbonate ions indicates that other substances are mixed in with the water.

The pH of the water is stated as 7, which indicates that the drinking water is neutral.

To calculate the mass of calcium ions in 250 cm³ of drinking water:

• The concentration of calcium ions is 60 mg per 1000 cm³.

• Therefore, for 250 cm³:

  ext{Mass of calcium ions} = rac{60 ext{ mg}}{1000 ext{ cm}^3} imes 250 ext{ cm}^3 = 15 ext{ mg}.

So, the mass of calcium ions in 250 cm³ of this drinking water is 15 mg.

Calcium is known to be a metal because it is located on the left side of the periodic table. Specifically, it is in group 2, where alkaline earth metals are found, which typically have metallic properties such as conductivity and malleability.